Just send 'em to me. I live in Florida, The Sunshine State. Who knows, you might even get them back!
Actually, there's another similar approach. Place the decals in a picture frame (8 1/2" x 11") and set the frame in the sun; you can move the frame to follow the sun, not be concerned about which direction the window faces, and minimize moisture accumulation. Make sure your frame has clear (not matte/non-glare) glass, and not plastic.
Place the frame (without the decals) in the sun for about an hour; this will dry out the glass and the backer board. Install the decals, and return the frame to the sunny area. You can even put shims on the bottom of the frame, tilting it so it directly faces the sun, not at an angle.